The present invention relates to the control of high pressure fuel supply pumps.
Gasoline direct injection (GDI) fuel systems typically impose extra costs on original equipment vehicle manufacturers compared to conventional multi-port injection (MPI) systems. In addition to the in-tank low pressure feed pump, GDI systems also require an engine mounted high pressure pump. The higher pressures required for the GDI systems have also proven to be audibly louder. In the past few years, there have been some gains in driving down the cost of the GDI fuel pump through simplification and size reduction. However, noise remains a key customer complaint.
Current state of the art GDI pumps as disclosed in Hitachi, U.S. Pat. No. 7,401,594 and Bosch, U.S. Pat. No. 7,707,996 employ a digital on/off-type solenoid control for accurately timing opening and closing of the inlet check valve with respect to the cam pumping ramp. In these types of pumps, the pumping chamber fully charges during every cycle. When the inlet check valve is opened a backflow of pumped fuel is spilled into the low pressure portion of the fuel circuit. Those embodiments suffer from high audible noise associated with the opening and closing impacts of the high speed on/off-type solenoid operated valve. Additionally, the backflow causes excess pressure pulsations in the inlet line that are countered by the pump supplier adding inlet pressure dampeners.